Methods of making and accessing cables having access features

ABSTRACT

Cables jacket are formed by extruding discontinuities in a main cable jacket portion. The discontinuities allow the jacket to be torn to provide access to the cable core. The discontinuities can be longitudinally extending strips of material in the cable jacket, and can be introduced into the extrudate material flow used to form the main portion through ports in the extrusion head. The discontinuities allow a section of the cable jacket to be pulled away from a remainder of the jacket using a relatively low peel force.

RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119 ofU.S. Provisional Application Ser. No. 61/546,597 filed on Oct. 13, 2011,the content of which is relied upon and incorporated herein by referencein its entirety.

This application is related to PCT/US11/34309 (Atty. Docket No.HI10-032PCT), filed Apr. 28, 2011, and to U.S. Prov. App. No. 61/407,744(Atty. Docket No. HI10-095P), filed Oct. 28, 2010, U.S. Prov. App. No.61/416,684 (Atty. Docket No. HI10-100P), filed Nov. 23, 2010, and toU.S. Prov. App. No. (Atty. Docket No. HI11-104P), filed Oct. 13, 2011,each of which is incorporated by reference herein in its entirety.

BACKGROUND

1. Field of the Disclosure

A fiber optic cable is disclosed, specifically a fiber optic cablehaving access features for accessing a core of the fiber optic cable.

2. Technical Field

Fiber optic cables frequently require that the fibers inside areaccessed mid-span rather than at an end of the cable. This oftenrequires extensive cutting of the cable jacket to enable a portion ofthe jacket to be removed, allowing access to the fibers inside thejacket. Conventional cutting tools, such as box cutters or customcutting tools, can be cumbersome and dangerous, both to the operator andto the delicate optical fibers. Rip cords in a cable jacket can be usedfor cable access, but they add cost and require time and training inorder for the craftsman to use them properly. In one conventional accessprocess, a jacket is pierced using a first tool, and a second tool isused to “fish” out enough of the rip cord so that a third tool (e.g.,pliers) can grasp the rip cord. A pull force must then be applied to therip cord, tearing it through the jacket material. The jacket material isthen peeled away from the cable core and removed. If the rip cordbreaks, the cord must be “fished” out again.

BRIEF DESCRIPTION OF THE DRAWINGS

According to common practice, the various features of the drawingsdiscussed below are not necessarily drawn to scale. Dimensions ofvarious features and elements in the drawings may be expanded or reducedto more clearly illustrate the embodiments of the invention.

FIG. 1 is a partial cutaway view of a fiber optic cable according to afirst embodiment.

FIG. 2 is a cross-section of the cable jacket illustrated in FIG. 1.

FIG. 3 is an isolated cross-sectional view of one of the discontinuitiesin the cable jacket of FIG. 2.

FIG. 4 is a cutaway view of a portion of a coextrusion apparatus used tomanufacture cables with discontinuities.

FIGS. 5A-5C illustrate a process for accessing the end of a cable asillustrated in FIG. 1.

FIGS. 6A-6C illustrate a process for mid-span access for a cable asillustrated in FIG. 1.

FIGS. 7A-7B illustrate a method of manually determining peel force inthe cable of FIG. 1.

FIG. 8 illustrates a method of determining peel force in the cable ofFIG. 1 using a force measuring machine.

DETAILED DESCRIPTION

Reference is now made in detail to the present preferred embodiments ofthe disclosure, examples of which are illustrated in the accompanyingdrawings. Whenever possible, identical or similar reference numerals areused throughout the drawings to refer to identical or similar parts.

FIG. 1 is a partial cutaway view of a fiber optic cable 10 according toa present embodiment. The cable 10 comprises a core 20 surrounded by ajacket 30. The jacket 30 has an interior surface 34 that faces the core20, and an exterior surface 38. The jacket 30 can be formed primarilyfrom polymer materials, and can be generally referred to as “polymeric.”In this specification, the terms “polymer” and “polymeric” indicatematerials comprised primarily of extrudable polymer materials such as,for example, copolymers, but allows for the presence of non-polymermaterials such as additives and fillers. The core 20 can be, forexample, an assembly or arrangement having data-transmission and/orpower-transmission capabilities. In the illustrated embodiment, the core20 includes a bundle of optical fibers 40 bundled within contrahelicallywound binders 44, 46, the optical fibers being capable of conveyingoptical data.

The jacket 30 includes a separation feature that facilitates access tothe core 20. In the exemplary embodiment, the separation feature is apair of extruded discontinuities 50 that extend along the length of thecable 10. In this specification, the term “discontinuity” indicates aportion of the jacket 30 of different material composition than the mainportion of the jacket 30, the main portion being indicated by referencenumber 55. The main portion 55 can essentially be an annular hoopsurrounding the core 20, with the discontinuities 50 extendinglongitudinally through the main portion 55 along a selected length ofthe cable 10. According to one aspect, the discontinuities 50 providelines of weakness that allow the jacket 30 to be separated as shown inFIG. 1. The illustrated discontinuities 50 extend along the entire cablelength, although shorter lengths, such as 20 cm or more, may be used toprovide access to the core 20.

FIG. 2 is a cross-section of the jacket 30 in isolation, taken on aplane perpendicular to a length of the cable 10. In the exemplaryembodiment, the discontinuities 50 are bonded to the main portion of thejacket 55 when the jacket 30 is extruded. The illustrateddiscontinuities 50 are wholly embedded in the main portion 55, but oneor both ends of the discontinuities may extend to either jacket surface.The main portion 55 and the discontinuities 50 can be formed fromextrudable polymers, so that as the extrudates used to form the mainportion 55 and the discontinuities 50 cool and solidify, the extrudatesbecome bonded to a desired degree at an interface on each side of adiscontinuity 50. When the discontinuities 50 are formed while extrudingthe main portion 55 of the jacket, the bond between discontinuity 50 andthe remainder of the jacket 30 can be generally described as enabled bypolymer chain entanglement as the jacket 30 solidifies. The jacket 30accordingly comprises a cohesive composite polymer structure. The cablejacket 30 can also include tactile locator features 60, such as raisedsurfaces, or ‘bumps’, or depressed surfaces such as ‘divots’ orchannels, that provide a tactile indication of the location of thediscontinuities. A visual indication such as a stripe could also beextruded over the location of the discontinuities so that theirlocations are apparent from the cable exterior. Tactile or visualindicators can extend along the entire length of the cable, or alongselected lengths. One or more strength members, such as glass-reinforcedplastic (GRP) rods or metallic wires can be included at one or morelocations in the jacket 30.

The discontinuities 50 can be strips that may each occupy up to, forexample, 5% of the total jacket cross-sectional area AJ. In exemplaryembodiments, discontinuities 50 can be relatively narrow strips in thejacket 30, and may occupy relatively small portions of the jacketcross-sectional area AJ. For example, the discontinuities 50 can havecross-sectional areas AD that are less than 3% of AJ. In the illustratedembodiment, the discontinuities 50 each have cross-sectional areas ADthat are less than 2% of AJ. In FIGS. 1 and 2, two discontinuities 50are formed in the jacket 30 to facilitate opening of the jacket as shownin FIG. 1. Depending on the form that the core 20 takes, the number,spacing, shape, composition and other aspects of the discontinuities 50can be varied. For example, a single discontinuity in the jacket 30 maybe sufficient to allow the cable jacket 30 to be peeled away from thecore 20.

FIG. 3 is an isolated view of one of the discontinuities 50 in thejacket 140. A discontinuity 180 can have a maximum width A, a height B,and a center spacing from the jacket interior surface 34 of D. Thejacket thickness is C. According to one aspect, the aspect ratio A:B isin the range of 1:4 to 1:100. In general, lower aspect ratios A:B, whichindicates narrower discontinuities, are favorable in cablecross-sections as shown in FIG. 1. It is these discontinuities thatallow for a stress concentration to develop at the root of adiscontinuity and thus initiate failure of the primary jacket material.The illustrated ratio B:C is about 1:2, which indicates that the heightof a discontinuity is about half of the jacket thickness. The ratio B:Cis selected to provide ease of access to the core and to maintainsufficient robustness of the cable 110, and will vary with factors suchas the fracture toughness of the material of the primary portion 55, thebond between the discontinuities 50 and the primary portion 55, andother factors. According to one embodiment, the ratio B:C is at least1:4, or, stated alternatively, B is at least ¼ of the jacket thickness Cat the centerline of the cable. If an extremely thin, “film” typeembodiment of discontinuity 50 is included, the maximum width W of adiscontinuity can be in the range of 0.2 mm or less, and may be about0.1 mm.

The materials and processes used to form the main portion 55 and thediscontinuities 50 can be selected so that the interfaces therebetweenallow for relatively easy access to the core 20 by peeling back thejacket 30 as shown in FIG. 1. The cable 10 may be constructed to meetother requirements for robustness, such as requirements for the jacket30 stay intact under tensile loads, twisting, in temperature variations,and when subjected to other known cable test criteria, such as, forexample, ICEA 460, and GR20.

The cable jacket main portions 55 and the discontinuities 50 describedin this specification may be made from various polymer materials. Eitherthe main portion 55 or the discontinuities 50 may be made frompolypropylene (PP), polyethylene (PE), or blends of materials such as ablend of PE and ethylene vinyl acetate (EVA), flame-retardant materialsuch as flame-retardant polyethylene, flame-retardant polypropylene,polyvinyl chloride (PVC), or polyvinylidene fluoride (PVDF), filledmaterials such as polybutylene terephthalate (PBT), a polycarbonateand/or a polyethylene (PE) material and/or an ethylene vinyl acrylate(EVA) or other blends thereof having fillers like a chalk, talc, or thelike, and other materials such as a UV-curable acrylates.

In the exemplary embodiments, the main portion can be extruded from afirst extrudable polymeric material comprising at least 80% of a firstpolymer, polyethylene, by weight, and the discontinuities can beextruded from a second extrudable polymeric material comprising at least70% of a second polymer, polypropylene, by weight and additionally atleast 0.5% of the first polymer polyethylene by weight. Higher amountsby weight of the first polymer may be included in the second material,such as at least 1.0%, or at least 2%. Without being bound by theory,Applicants believe the bond between polypropylene and polyethylene maybe caused by one or both of quantities of ethylene that are compoundedin the polypropylene bonding with the polyethylene, and molecularentanglement between the PE and PP. According to this understanding, theamount of ethylene in the PP extrudate can be increased to increase thebond between the discontinuities and the remainder of the jacket. In oneembodiment, the main portion 55 is made from a first polyethyleneextruded material, such as a medium density polyethylene (MDPE). Thediscontinuities 50 are made from a second, polypropylene/polyethyleneblend of extruded material, the blend including from 6% to 20%polyethylene, with the remainder of the blend being primarily apolypropylene material. The first polymer material can be, for example,a unimodal or bimodal type polyethylene defined by its molecular weightdistribution, with the lower molecular weight polymer chains increasingbond strength at the interface of the jacket and the feature (throughthe process of promoting entanglements and co-crystallization).

FIG. 4 is a cutaway section view of a coextrusion flow diverter 300 thatcan be used in conjunction with an extrusion crosshead commonly used toform an annular jacket such as the jacket 30 shown in FIG. 2. The flowdiverter can be a modification of an existing component of an extrusionapparatus. In such an extrusion apparatus, the extrusion tip and die aredirectly downstream of flow diverter 300. The arrows 1 in FIG. 4illustrate the flow direction of a first molten extrudate, and thearrows 2 indicate the flow direction of a second molten extrudate. Theflow diverter 300 has an exterior surface 320 over which flows the firstmolten extrudate material that is used to form the main portion 55 ofthe jacket 30. The diverter 300 includes a pair of struts or fins 330,each having a port 340 that allows introduction of the second moltenextrudate material used to form the discontinuities 50 into the flow ofthe first molten extrudate. The flow diverter 300 acts to divide thefirst material around the ports 340 supplying the second material. Thefirst and second extrudate materials join downstream of the flowdiverter 300. As the first and second materials are extruded, a core(not shown) including one or more optical fibers advances along thecenter line CL in the process direction P. The first and secondextrudate materials draw down, cool, and solidify around the fiber opticcore advancing through the crosshead to form the jacket 30. The tactilelocator features 60 can be included by forming an exterior radius in theextrusion die. If desired, strength members, such as the strengthmembers 66, can be introduced into the extrusion process and embedded inthe jacket 30.

FIGS. 5A-5C illustrate a process for accessing the end of a cable asillustrated in FIG. 1. Referring to FIG. 5A, a technician uses a tool500 such as side cutters or pliers to pinch the cable is pinched acrossless than 180 degrees of arc of the cable exterior, such as between ofthe features 60. The blades of the tool 500 are oriented to pinch thesame side of the cable 10, as delineated by the locator features 60.Pinching one side of the cable 10 causes the cable jacket 30 to beginseparating at the discontinuities 50. Referring to FIG. 5B, afterseparation is initiated, a section 520 of the jacket 30 located betweenthe discontinuities 50 is pulled away from the remainder of the jacket30. Tearing can be facilitated by twisting the section 520. Referring toFIG. 5C, the technician tears the section 520 for a desired length usingthe tool 500. The core 20 is then accessible for connectorization, etc.

FIGS. 6A-6C illustrate a process for mid-span access for a cable asillustrated in FIG. 1. Referring to FIG. 6A, a technician uses a razortool 600 to form a ring cut in the jacket 30 that is approximately ¾ ofthe jacket thickness. The cable 10 is then flexed to break the remainingjacket material. While a razor blade tool is used in this step, it isthe sole step in which a very sharp bladed tool is used, as opposed tomultiple steps in conventional access methods. Referring to FIG. 6B, thetechnician shaves the jacket at each of the two locator features 60 witha sheath removal tool 650. The tool can be, for example, Corning CableSystems' Cable Sheath Removal Tool, Catalog #RPXS-000. The jacket 30only needs to be shaved for approximately six inches, on only one sideof the ring cut line. Referring to FIG. 6C, the cable 10 is flexed toinitiate the separation of the two jacket halves. The core 20 is thenaccessible for connectorization, etc.

According to the present embodiments, one or more discontinuities in acable jacket can be arranged to provide relatively easy access to acable core. The ease of access can be defined, for example, by the forcerequired to pull, or peel away a section of the cable jacket at one ormore discontinuities. The peel force can be measured as a direct forcemeasurement, in Newtons, of the force a person must exert as the jacketsection is peeled away from the cable core. It is understood that thejacket will not be perfectly uniform, and that a person or machinecannot exert a perfectly uniform force as the jacket is peeled, so “peelforces” described in this specification indicate an average forceexerted as a distance of the jacket section is peeled back. It is alsounderstood that peel forces according to the present embodiments aremeasured without any additional modifications to the cable jacketexterior, such as by scoring. The peel forces can be relatively low whencompared to the forces required to access a cable without extrudeddiscontinuities. For example, a peel force may be less than about 90Newtons (N). In exemplary embodiments, the peel force required may befrom about 20N to about 65N. Peel forces are defined herein to includeany force great enough to cause the jacket material to rip, tear, orotherwise separate along the discontinuities 50 for accessing the cablecore.

It is relatively easy to measure peel force. FIGS. 7A and 7B steps in amethod of illustrating peel force in the cable 10 of FIG. 1. Using cable10 as a reference, about 25 mm of jacket is cut away from one end of thecable 10. The ends of the cable 10 are secured to a bench or othersturdy surface. A small hole is placed in the jacket proximal to theedge of the jacket where it was cut away from the core, as shown in FIG.7A, and one end of an “S” hook is inserted into the hole in the jacket.If the cable includes a pair of spaced discontinuities, the hole isformed midway between the two discontinuities. A lanyard or wire isattached to the other end of the S hook. The lanyard is fixed to a forcegauge, such as a Chatillon gauge available from Ametek Test andCalibration Instruments of Largo, Fla. As shown in FIG. 7B, the forcegauge is pulled by hand or by some mechanical means, away from the cableat an angle of 45 degrees to the cable centerline, until the section ofthe jacket attached to the S hook peels away from the rest of thejacket. The jacket section is pulled for a distance of 250-500 mm awayfrom the initial jacket removal location. The average peel can becalculated as the average force measured by the force gauge as thejacket section is pulled along the selected distance.

In an alternate method of measuring peel force, a force testing machine,such as those available from Instron®, pulls the section of cable awayfrom the remainder of the cable at angle of 90 degrees to the remainderof the cable 10. This machine is shown in FIG. 8. The cable 10 issecured to a linear slide that translates the cable beneath the portionof the machine that is secured to the jacket section being peeled away.In this arrangement, the cable 10 slides beneath the force gauge thatmeasures the tension on the section being removed, so that the sectioncan be peeled away at a 90 degree angle. The tension in the removablesection can be averaged over a desired distance to obtain the averagepeel force.

In general, the separation properties disclosed in this specificationmay be obtained by coextruding the discontinuities from a differentmaterial than the material used to form the main portion of the jacket.As an alternative method, the discontinuities may be made from the samematerial as the remainder of the jacket, but subjected to differentcuring conditions, for example.

What is claimed is:
 1. A fiber optic cable, comprising: a corecomprising an optical fiber; a jacket surrounding the core, wherein thejacket has an interior surface that faces the core and an exteriorsurface, wherein the jacket is formed primarily from a polymer material,wherein the jacket comprises: a discontinuity extending lengthwise alongthe cable and wholly embedded in the jacket, wherein the discontinuitycomprises a portion of the jacket of a different material compositionthan a main portion of the jacket, the main portion of the jacket beingan annular hoop surrounding the core, whereby the discontinuity providesa line of weakness that allows the jacket to be separated to provideaccess to the core, and wherein the discontinuity is bonded to the mainportion of the jacket such that the jacket comprises a cohesivecomposite polymer structure.
 2. The fiber optic cable of claim 1,wherein the jacket comprises at least one of a tactile indicator and avisual indicator extending lengthwise along the exterior of the jacketdenoting the location of the wholly-embedded discontinuity of thejacket.
 3. The fiber optic cable of claim 2, wherein the at least one ofa tactile and visual indicator comprises a tactile locator featurecomprising at least one of a raised surface and a depressed surface onthe exterior of the jacket to provide tactile indication of the locationof the discontinuity.
 4. The fiber optic cable of claim 3, wherein thetactile locator feature comprises a raised surface in the form of a bumpto provide tactile indication of the location of the discontinuity. 5.The fiber optic cable of claim 4, wherein the bump extends along theentire length of the cable.
 6. The fiber optic cable of claim 1, whereinthe discontinuity has a maximum width and height, and wherein the ratioof the maximum width to the height of the discontinuity is in the rangeof 1:4 to 1:100, thereby facilitating stress concentration at a root ofthe discontinuity.
 7. The fiber optic cable of claim 6, wherein theratio of the height of the discontinuity to the overall thickness of thejacket is at least 1:4.
 8. The fiber optic cable of claim 1, wherein themain portion of the jacket is formed from a first material comprising atleast 80% by weight of a first polymer, and wherein the discontinuity isformed from a second material comprising at least 70% by weight of asecond polymer and at least 0.5% by weight of the first polymer, therebyincreasing bonding between the discontinuity and the main portion of thejacket.
 9. The fiber optic cable of claim 8, wherein the first polymeris polyethylene and the second polymer is polypropylene.
 10. The fiberoptic cable of claim 9, wherein the second material comprises at least1% by weight polyethylene.
 11. The fiber optic cable of claim 9, whereinthe second material comprises at least 2% by weight polyethylene. 12.The fiber optic cable of claim 1, wherein the discontinuity is a firstdiscontinuity and further comprising a second discontinuity whollyembedded in the jacket and spaced apart from the first discontinuitysuch that a section of the jacket is between the first and seconddiscontinuities.
 13. The fiber optic cable of claim 12, wherein a peelforce is required to pull the section of the jacket away from theremainder of the cable at an angle of 90-degrees to the remainder of thecable, and wherein the peel force is less than about 90 Newtons (N). 14.The fiber optic cable of claim 13, wherein the peel force is in a rangefrom about 20N to about 65N.
 15. A method of making a cable, comprising:advancing a core in a first direction, the core including at least oneoptical fiber capable of conveying communication signals; and extrudinga jacket around the core, the extruding comprising: introducing a firstpolymeric extrudate material into the extrusion apparatus; introducing afirst flow of a second polymeric extrudate material into the firstpolymeric extrudate material through a first port; introducing a secondflow of extrudate material into the first polymeric extrudate materialthrough a second port; and allowing the first and second extrudatematerials to draw down and cool around the core, the first polymericextrudate material forming a main portion of the jacket, the first flowforming a first discontinuity in the main portion, and the second flowforming a second discontinuity in the main portion, wherein the firstand second discontinuities are at least partially embedded in the mainportion, wherein a section of the jacket located between the first andsecond discontinuities is separable from a remainder of the jacket by apeel force on the section of less than 90 Newtons (N).
 16. The method ofclaim 15, wherein the first discontinuity is wholly embedded in the mainportion.
 17. The method of claim 15, the jacket having an annularcross-section with an interior surface and an exterior surface with ajacket thickness therebetween from 0.5 mm to 2.0 mm, and wherein across-sectional area of each discontinuity is less than 5% of across-sectional area of the jacket.
 18. The method of claim 15, whereinthe first extrudate material includes a first polymer and the secondextrudate material includes second polymer, the second extrudatematerial further including between 1% to 20% by weight of the firstpolymer.
 19. The method of claim 15, further comprising advancing anelongate strength member along the first direction, wherein the jacketis extruded around the strength member.
 20. The method of claim 15,wherein the first discontinuity has a maximum width measuredperpendicular to a radius passing through the first discontinuity thatis less than 0.2 mm.